1. Place the biscuits in paper bag and crush finely with a rolling pin. Melt the butter, stir in the crushed biscuits and Demerara sugar. Mix well and press into the bottom of a 20 cm/8 in loose-bottomed cake tin.
2. Sprinkle the gelatine over the orange juice in a bowl. Place over a saucepan of boiling water and stir occasionally until the gelatine has dissolved. (Alternatively place the bowl in a microwave oven on DEFROST setting until the gelatine has dissolved.) Leave to cool.
3. Cream the curd cheese, cream cheese and sugar together until smooth. Stir in the orange rind.
4. Mix the dried egg white and half the water until smooth, then gradually blend in the remaining water. Whisk until stiff.
5. Stir the cooled gelatine mixture into the cheeses, then lightly fold in the whisked egg white. Turn into the tin, level the top and chill until firm.
6. To serve, loosen the cheesecake from the sides of the tin with a knife, then push up the base and place the cheesecake on a dish. Decorate with fresh or jelly orange slices